In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsically doped material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n type extrinsically doped material wafers, and implanting materials such as boron or indium creates p type extrinsic material portions in a semiconductor wafer. Within the ion implantation chamber silicon wafers are physically impacted by the ion beam.
One method for ion implantation of silicon wafers uses a combination of a broad ion beam that that is wider than the maximum diameter of the wafer and a mechanism for mechanically scanning or moving the wafer in a direction that is orthogonal to the broad direction of the beam. The broad beam can be generated either as a continuous, static “ribbon” beam from an ion source or the beam can be the result of a “pencil” beam that is scanned back and forth by a beam scanning mechanism across the workpiece. The broad beam is ideally supposed to strike the wafer so that the angle between the path of the ions and the workpiece surface (i.e., angle of incidence) is the same at every point on the workpiece. However, the ions may not all be moving in the identical direction across the entire width of the wafer due to problems that are inherent in the generation and focusing of broad types of ribbon beams, for example. The resulting non-parallel paths of the ions results in implantation angle errors. A method for measuring the angle of the ions is required to verify that the implant angle error will be within a specified value or range of values before conducting the implant so that a proper process is assured.
Typically, a mask with multiple apertures has been placed in front of a beam current measuring device known as a profiler that only allows ions through it at defined locations across the broad width of the beam. If the ions are all moving in the same direction, the profiler will record beamlet positions along the profiler path identical to each aperture position as it travels behind a mask in the broad direction of the beam. In addition, if the mask is calibrated to the profiler, the overall direction of the ions can be measured, since the peak of the current measurement should occur when the profiler is positioned directly behind the mask aperture. However, if the paths of the ions are not all parallel to one another, the profiler will measure varying beamlet positions as it transverses behind the multiple apertures of the mask. One particular problem with this method is that it can only measure the beam angle at each defined aperture location. Another disadvantage lies in the need for a mask as wide as the ribbon beam it needs to measure, typically resulting in a large and costly assembly.
An exemplary prior art beam angular measurement system assists semiconductor device fabrication by measuring ion beam current and angle of incidence at various locations within an ion beam. A moveable detector is operative to provide uniformity measurements before ion implantation (e.g., performing calibration in situ during verification). Based on the various measurements, generation of the ion beam can be modified to improve uniformity. The ion implantation can be performed with improved uniformity and with tighter process controls.
The prior art figure illustrated in FIG. 1 is a simplified schematic of a single wafer ion implantation system 100. The prior art system 100 contains an ion chamber 102, an ion beam generating mechanism 104, a uniformity detector 106 (should be moveable as in FIG. 5), and a pedestal or platen 110 for temporarily capturing the workpiece/wafer 108. The ion beam generating mechanism 104 normally generates a ribbon ion beam 112, with characteristics including beam current, angle of incidence, and the like. Although the ion beam 112 is depicted as being substantially orthogonal to a surface of the wafer 108, the ion beam 112 can be at other incident angles with respect to the surface of the workpiece 108. The pedestal 110 can move the wafer 108 through the ion beam 112 at a controlled velocity to achieve the preferred implantation. An ion implantation can be performed in a single pass of the wafer 108 through the ribbon ion beam 112. A uniform implantation is obtained because the entire wafer 108 moves through the ion beam 112 at about the same rate.
The uniformity detector is typically parked outside of the ion beam until it is used. This prior art device can include any suitable number of detectors, detectors located at other positions, and movable detectors. The detector 106 may be reside in substantially the same plane as the wafer 108. The detector 106 measures uniformity of beam current across the width of the ion beam 112 at a finite number of locations. When combined with an angle mask, typically as wide as the wafer and positioned in the beam such that only a few beamlets pass through the mask, the prior art detector 106 can acquire angle of incidence measurements of the ion beam 112 at the finite number of locations and the beam current uniformity and angle of incidence measurements can be utilized to adjust the ion beam 112 to improve uniformity. Additionally, these measurements can be used to determine potential damage to the wafer when the measurements depict substantial deviations from desired properties. One of the difficulties with this approach is that the mask has a predetermined number of slots and therefore the angle of incidence can only be measured along a portion of the ion beam and not the entire beam 112.
Another exemplary detector, described in U.S. Pat. No. 6,989,545 includes a series of elements that respectively include an aperture and a pair of beam current sensors. The aperture permits only a portion of the ion beam 112, referred to as a beamlet, to pass through to impact the pair of beam current sensors. The sum of beam currents measured by each of the pair of sensors is employed to determine a total beam current at the aperture location, and an angle of incidence of the beamlet can be calculated from the difference of beam currents of each sensor. Accordingly, the measurements of the elements can then be used to determine uniformity of the ion beam and each of the elements can be utilized to obtain an angle of incidence measurement throughout the ion beam 112.
Based on these angular measurements, corrective actions can be taken to improve angle uniformity of the ion beam 208.
Both of the systems mentioned supra have problems associated with them. Prior art FIG. 1 measures the beam angle only at the location of slots in the mask. One particular problem with prior art FIG. 2 is that it can only measure the beam angle at each of the defined aperture locations, and the beam angle is not measured continuously.
Therefore, a need exists in the art for a method and system that generally decreases the aforementioned issues and provides for measuring the beam angle at any point along the broad direction of the beam.